Best Block for 400hp turbo conversion? M20 or M50?

[RacingG]

Hi Guys, I'm planning an e30 turbo project with a target of 400hp.
At the moment and as a baseline am planning to go the same way as the I've seen some swedes go and use an m20 2.5 block, m50 rods and m42 pistons, I think it needs the m20 diesel oil pump as well.. management will be megasquirt or emerald.

I'm planning to close the deck up on the block and wire ring it to get the seal. I'm planning for 1.5 bar (21 ish Psi)

My questions are:
1)whats the best way of lowering compression if it needs to be done? machining the piston crowns?

2) I was wondering if a better base would be an m50 2.5 block for the 4 valve head, is this a good idea or is the alloy block not up to it?

any general comments/ thoughts gratefully received.

Jimbo

[Gunni]

M50 engine clearly.
They where not alloy.

Otherwise a M20 with a healthy sized turbo will require about 15-18psi boost to reach 400hp.
I´d reccomend ARP studs , MLS gasket, better clutch,
That should do it,

No need for the M42 pistons or rods, or the diesel pump,

[RacingG]

My mistake on the block.. still learning about BMW engines again after a bit of a break.

Why do people use the M42 pistons and M50 rods if there is no need?

400 is a minimum but I want to get the block as bullet proof as possible and capable of more power, so want to eliminate all the weak points where possible.

I just want to keep this thread for the motor at the moment - obviously the clutch and diff will have to be uprated, and suspension/ brakes.

[Gunni]

Maybe they where looking for a way to lower compression with easily available parts?

Getting 400hp will be easier with a turbo cam, healthy turbo, engine management.

What is the use of the engine?
Long time racing
Short quarter mile

Those will really be what dictates how the engine gets built.

[RacingG]

Ahhh yeah, that makes sense - those pistons in the M20 block are lower comp. I assume the M50 rods are stronger. (they look it!)

Engine will be used in a project car as a business demo car. It will see some tracktime and do some drifting - generally driven hard and not really daily driven.

currently fancying putting it in a touring :O)

[Jhonno]

definately needs to be a turbo'd m50! better engine out the block..

[Laimis]

My recommendations: for low boost and power stock M20, for big power M50 (more realiable, 4 valve, etc.).